Is it a series cart or an IQ, if it is a series cart you may have a bad microswitch, on the back side of the forward, reverse lever there are three microswitches stacked up together, one is the backup horn, on is for half speed reverse, and I can't remember what the other is for but if your half speed revers switch isn't working it may be the problem. I am sure someone else will jump in here to help you further.